1. Field of the Invention
The present invention relates to a method and a device for monitoring torque output of a drive unit.
2. Description of Related Art
A control unit for the drive unit of a motor vehicle is known from published German patent document DE 103 20 017, the control unit in particular controlling or regulating the drive unit in regard to an output drive torque and the drive unit being an internal combustion engine of a motor vehicle. The motor vehicle typically includes a driver input transmission device actuatable by the driver of the motor vehicle, in particular a gas pedal actuatable using the foot. This is provided to output an output signal representing an instantaneous actuation state of the driver input transmission device. A control unit receives the output signal from the driver input transmission device and assigns the received output signal at least one setpoint output variable, which is in particular a setpoint drive torque of the drive unit. The drive unit is activated by the control unit in such a way that an actual output variable output by the drive unit approximates the setpoint output variable. Control units of this type are known in various designs for typical motor vehicle engines, in particular gasoline engines and diesel engines, e.g., Bosch engine-control systems having an electronic gas pedal (EGAS).
Furthermore, performing continuous torque monitoring to discover malfunctions in control units is known. This is used to protect passengers in the motor vehicle and to protect external traffic participants. Unintended acceleration of the vehicle is to be avoided by continuous torque monitoring. The core of continuous torque monitoring is a comparison of an actual torque provided by the engine to a permissible torque. In the normal case, the actual torque is less than the permissible torque. If the actual torque exceeds the permissible torque, an error exists in the engine control unit, and an error response resulting in a safer vehicle state is initiated. Monitoring of the engine control unit is typically performed according to a 3-level monitoring concept. The engine control itself, in particular presetting the setpoint torque, is performed in the first level, referred to as the functional level. The second level (monitoring level) is implemented as continuous torque monitoring. In this level, a permissible torque is ascertained as a function of vehicle and engine functions, inter alia, and compared to an actual engine torque. The second level is made secure in a complex manner, e.g., by double saving of all variables, cyclic RAM and ROM testing, program sequence controls, and command tests. The third level is used for computer security.
Published German patent document DE 197 39 565 discloses a method for controlling the torque of a drive unit of a motor vehicle, in which the torque of the drive unit is set at least according to the measure of the driver input, the actual torque of the drive unit being determined and a maximum permissible torque being ascertained at least on the basis of the driver input. A torque reduction and/or torque limiting occurs if the maximum permissible torque is exceeded by the actual torque. At least one operating state is established in which the torque of the drive unit is increased due to additional load. During this at least one operating state, the maximum permissible torque is increased. In particular, the permissible torque is thus increased during operation with a cold drive unit and/or during operation of high-load consumers.
The described methods for torque monitoring originating from the related art may not be transferred to hybrid vehicles without further measures. In hybrid vehicles, at least one further torque source (motor) is used in addition to an internal combustion engine. In most cases, it is an electric drive. In the engine controller, the desired torque requested by the driver, which is set by operation of a gas pedal, must be distributed to the existing torque source, which includes at least two motors. This is performed as a function of numerous surroundings variables, inter alia, with the goal of setting the operating point which is most favorable for consumption for all torque sources, i.e., drive motors. The core of the above-mentioned continuous torque monitoring is the torque comparison in the second level, the monitoring level, in which a permissible torque of the second level (monitoring level) is compared to an actual torque in the second level (monitoring level). If the actual torque exceeds the permissible torque, a corresponding error response is initiated. The calculation of the permissible torque in the second level (monitoring level) forms the functionality of the first level, the functional level. In the second level (monitoring level), the calculations from the first level (functional level) are performed once again, but greatly simplified, to reduce possible errors. In hybrid vehicles, a torque request (setpoint torque) is sent to the individual torque sources, i.e., the motors, by the vehicle controller. The actually output torque (actual torque) may deviate from this setpoint torque, however, because the motor control units may have intrinsic functionalities which elevate torque, such as idling regulators and auxiliary system compensators. In addition, the inertia of the torque sources of the motors causes a dynamic torque deviation. These deviations must be simulated in the calculation of the permissible torque in the second level (monitoring level) to prevent erroneous response of the torque monitoring unit. This represents a high level of complexity in regard to the development and calibration of the second level.